The present invention relates to a packet relay apparatus, and more particularly to a bandwidth policing technique for an apparatus having a congestion notification function.
In response to the U.S. government's recommendation on network neutrality and, reflecting this background, rising discussions regarding fair bandwidth allocation by the Internet Engineering Task Force (IETF), congestion notification techniques, such as the one taken up in RFC3168, “The Addition of Explicit Congestion Notification (ECN) to IP” (http://www.ietf.org/rfc/rfc3168.txt) (Non-Patent Document 1), are coming into the limelight.
ECN is a congestion notifying technique to cause the occurrence of congestion in a packet relay apparatus, such as a router/switch constituting part of a network, to be expressly notified by the router/switch itself to transmitting/receiving terminals.
The congestion control function according to the conventional Transmission Control Protocol (TCP) (RFC2581, “TCP Congestion Control”, (http://www.ietf.org/rfc/rfc2581.txt) (Non-Patent Document 2) has no means of explicitly notifying senders/receivers of the occurrence of congestion. For this reason, when a packet drop in the network is detected by a sender, the occurrence of congestion is autonomously determined. And, if the occurrence of congestion is affirmed, the congestion is avoided by restraining the transmission bandwidth available to the sender.